Two primary video format standards are utilized worldwide to record, transmit, and display composite video data, namely, the National Television Systems Committee (NTSC) and the Phase Alternating Line (PAL) standards. Both the NTSC and PAL standards define interlaced video systems in which one frame of display pixels is partitioned into alternating interlaced fields, with each interlaced field updated at twice the update rate of the frame. Additionally, many digital versatile disk (DVD) players, DVD player-recorders, and similar video recording and playback systems, output data in an interlaced format, depending on the format used to broadcast or record the given playback media.
On the other hand, many state of the art display systems, such as high definition television (HDTV) sets, generate displays using a progressive scan format. In the progressive scan format, video data are transmitted and displayed in frames, which are not partitioned into fields. In other words, each display frame is generated by sequentially scanning through all the lines of each frame at the original field update rate. Hence, in order to interface an interlaced video source, such as television cable interface or a DVD player playing-back an interlaced format DVD, with a progressive-scan display system, such as a HDTV set, deinterlacing must be performed.
Furthermore, films are typically produced with a frame rate of twenty four (24) frames per second, while in the PAL video system, frames are generated at a rate of twenty five (25) frames per second from interlaced fields at a rate of fifty (50) fields per second. During conversion of film to interlaced PAL video, the 2:2 pull-down technique is typically utilized to convert the film frames into interlaced fields, which are then used to reconstruct frames on the PAL display, in either an interlaced or progressive scan format. In particular, the frame rate of twenty four (24) frames per second is increased by four percent (4%) to generate frames at a rate of twenty five (25) frames per second. The 2:2 pull-down technique then converts the twenty five (25) frames per second data into fifty (50) fields per second data. Additional applications of the 2:2 pull-down technique include the conversion of computer generated images into interlaced video, and the conversion of thirty (30) frames per second film into sixty (60) fields per second interlaced video. For discussion purposes, a PAL system will be used as an example.
The 2:2 pull-down technique replicates the content of each film frame twice to generate identical odd and even interlaced video fields. In an interlaced playback system, these interlaced fields are each displayed at the PAL field rate of fifty (50) fields per second to generate full video frames at the PAL frame rate of twenty five (25) frames per second. The PAL frame rate is therefore slightly higher than the original film rate of twenty four (24) frames per second. For progressive scan systems, corresponding pairs of odd and even fields are weaved together to generate frames at the PAL interlaced frame rate of twenty-five (25) frames per second, and then each frame is repeated twice to generate a stream of frames at the progressive scan frame rate of fifty (50) frames per second.
In order to correctly generate either interlaced or progressive scan frames from interlaced PAL fields that were originally derived from film, the correct pairs of odd and even fields must be weaved together. Hence, some form of 2:2 mode detection must be performed to detect when a sequence of fields was originally generated from film with the 2:2 pull-down technique and subsequently identify the correct pair of fields that will be weaved together to compose each display frame.
Given increasing popularity of progressive scan display systems, as well as the need to maintain compatibility with systems generating interlaced display data, new 2:2 detection techniques are required. In particular, these deinterlacing techniques should allow for the generating of progressive scan displays from interlaced data created by 2:2 pull-down.